The present invention relates to a system for removing iron from a supply of water and, in particular, to a method, apparatus and system for simply and effectively filtering a drinking water supply to remove iron.
Many drinking water supplies contain elemental iron or iron compounds in either dissolved or suspended forms. Regardless of the form, very low concentrations of iron are known to cause a characteristic disagreeable taste and to result in a similarly characteristic red stain on fixtures and other utensils with which the water comes in contact. Concentrations of iron in water as low as 0.3 ppm are known to cause iron oxide stains and disagreeable taste.
Several basic methods are known in the art for treating water to remove iron. These include ion exchange, oxidation and filtration, and sequestration. Removal by ion exchange can often be effected through the use of a conventional water softener, if the iron concentration is fairly low. In a sequestration process, the iron is tied up in a complex molecule, such as a polyphosphate, where it is held and prevented from oxidizing. Oxidation and filtration are often combined in a single unit where a base material, such as a zeolite is treated with manganese which acts to convert soluble ferrous iron in the water to insoluble ferric hydroxide which is retained in the granular material by mechanical filtration. Such systems require periodic backwashing to remove the precipitated iron compounds and regeneration to restore the manganese oxide, such as by washing with potassium permanganate.
One type of zeolite which is commonly used in oxidation/filtration systems for iron removal is a manganese-treated sodium aluminosilicate in granular form. This material is typically utilized in a loose bed configuration with the granular material having a particle size substantially in the range of 8 to 50 mesh (approximately 0.5 to 3 mm). A bed depth of 2 to 3 feet may be required for residential drinking water systems and the relatively large particle size is desirable to minimize pressure drop across the bed in the filtering mode and to facilitate backwashing.
Although such manganese-treated zeolite systems can be most effective, they are relatively large and expensive and, furthermore, require more complex flow control systems to accommodate backwashing and regeneration. It would, therefore, be desirable to have an iron removal system which is less complex and expensive, but yet is effective and easy to maintain. In particular, an oxidation/filtration system which does not require backwashing and regeneration, yet will effectively reduce the iron content in water to below 0.3 ppm would be most desirable.